This disclosure relates generally to wind turbines, and more particularly to a control method and a control system for a wind turbine.
Recently, wind turbines have received increased attention as an environmentally safe and relatively inexpensive alternative energy source. With this growing interest, considerable efforts have been made to develop wind turbines that are reliable and efficient.
A wind turbine includes a control unit, a rotor having a plurality of blades, and a blade pitch driver for adjusting the blade pitch to keep the speed of the wind turbine rotor within operating limits as the wind speed changes. The blades are usually feathered to reduce unwanted rotational torque in the event of wind gusts or emergency shutdowns.
However, when a blade pitch runaway fault occurs, the faulted blade cannot be controlled by the blade pitch driver and may move towards either fine position or feather position at a high pitch angle rate. Under this circumstance, the control unit will initiate a shutdown procedure that moves the blade pitch angles towards full-feathered position. During the shutdown, the wind turbine will experience an aerodynamic imbalance on the rotor due to the difference in pitch angles between the different blades, resulting in imbalance loads on a tower top and a hub of the wind turbine.
In conventional wind turbines, aggressive shutdown strategies may lead to high mechanical loads on some components (e.g. a yaw bearing, a pitch bearing, a tower, and a foundation). In particular, in the case where a blade runs away to power or feather, a fast shutdown of the other healthy blades results in high imbalance moments. The imbalance moments excite other components as well (e.g. the yaw bearing, the pitch bearing, the tower, the foundation, and a drive train).
Conventional open-loop shutdown control approaches with a fixed, pre-defined pitch-out profile require specific manual tuning and optimization of control parameters for each different wind turbine configuration. Additionally, because a single pitch out strategy needs to deal with any initial pitch angle and any varying wind condition during the shutdown, suboptimal performance with high variation of the peak loads may occur.
Therefore, it is desirable to provide a system and a method to address at least one of the above-mentioned problems.